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From: gnb@bby.oz.au (Gregory N. Bond)
Newsgroups: comp.windows.x
Subject: Xt shared GCs, regions and expose processing
Message-ID: <1991May16.073250.14656@melba.bby.oz.au>
Date: 16 May 91 07:32:50 GMT
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Organization: Burdett, Buckeridge and Young Ltd.
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The Xt manual states that GCs obtained via XtGetGC() "must be treated
as read-only" (sec 11.4).  However, I have seen a couple of widgets
that do something like this in the widget redraw routine:

	if (region) XSetRegion(XtDisplay(w), w->widget.GC, region);

	....
	/* do the draw */
	....

	if (region) XSetClipMask(XtDisplay(w), w->widget.GC, None);

often with code to set region=NULL if it is clear it covers most of
the window.

This doesn't seem to be read-only, but from the point of view of
multiple widget instances that may share the GC, the clip region
is always None when the routine is entered.

It is clear that this code works, at least in my situation.  Is it
"legal" to do so?  If not, how should complex widgets handle expose
events if they cannot legally set the clipmask in shared GCs but still
want to avoid flicker from a full redraw?

Greg.
--
Gregory Bond, Burdett Buckeridge & Young Ltd, Melbourne, Australia
Internet: gnb@melba.bby.oz.au    non-MX: gnb%melba.bby.oz@uunet.uu.net
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